1. Field of the Invention
The present invention relates to a method for detecting an operating state of a fluid chamber of an inkjet print head, wherein a generated pressure wave is detected and analyzed.
2. Background of the Invention
In a known inkjet printing apparatus having an inkjet print head, the inkjet print head comprises an inkjet fluid chamber. In the fluid chamber, an inkjet fluid is held. The fluid chamber comprises at least one opening, commonly referred to as a nozzle or orifice, through which a droplet of the fluid may be ejected. Ejection may be induced by one of a number of known techniques. For example, local heating of the inkjet fluid may be used to generate a gas bubble due to which a pressure is induced in the fluid chamber resulting in a droplet of fluid being ejected through the nozzle. In another known print head, an electromechanical transducer such as a piëzo-element is used to generate a pressure change in the fluid chamber for ejecting the droplet of fluid.
For print quality, the ejection of an inkjet fluid droplet may be critical. In particular, a droplet may be ejected under an incorrect angle and/or at an incorrect speed or may not be ejected at all due to dirt, air or any other disturbance in the fluid chamber. Further, if the inkjet printing apparatus is used for certain applications, incorrect ejection may lead to an unusable result. Therefore, it is advantageous to determine whether a fluid chamber is in a good operating state and, if it is determined that a fluid chamber is not in a good operating state, using another fluid chamber to eject a droplet at the intended position, for example.
In order to determine whether a fluid chamber is in a suitable operating state, i.e. whether there are no obstructions or disturbances in the fluid chamber, detection of the acoustics of the fluid chamber may be employed. Any chamber has a predetermined acoustic behavior. If a pressure wave, such as an acoustic wave, is introduced in the fluid chamber, the pressure wave will reflect and damp in the fluid chamber over time. Detecting the response to the generated pressure wave allows the presence of objects to be examined, such as dirt or air bubbles or the like, in the fluid chamber. Such a method and a corresponding device are known from the background art.
In the background art, the detected, resulting pressure wave is compared with a reference pressure wave, obtained from an undisturbed fluid chamber. If in the comparison, significant differences are determined, the fluid chamber may be considered to be disturbed and therefore the fluid chamber may be considered to be in an inoperative state. However, such a determination method is sensitive to noise and other measurement imperfections. Further, a quick comparison leads to incorrect determinations, i.e. incorrectly determining that a fluid chamber is in an inoperative state or incorrectly determining that a fluid chamber is in an operative state. A number of incorrect determinations may be decreased by suitable signal processing, which inevitably leads to a relatively long processing time. However, it is desirable to determine the operating state prior to a subsequent use of the same fluid chamber.